The present invention relates to an automatic exposure control device for a photographic camera with storage of an electronic value analogous to the diaphragm to be set and with an electronic triggering of the shutter closing process.
An automatic exposure control device in photographic cameras can be designed either so that the user preselects the diaphgram, whereupon the time is automatically formed upon triggering of the camera (automatic timing); or the control device can be constructed so that the user preselects the time, whereupon the diaphragm closes automatically to the value corresponding thereto (automatic diaphragm).
It has been known to produce, in the exposure control device, voltages logarithmically analogous to the individual exposure parameters and to process these values by calculation by means of addition and subtraction. Furthermore, it has already been suggested to provide a storage means in the camera and to store a voltage therein which is analogous to one of the exposure parameters, and to make available, in correspondence with the storage condition, an RC combination which closes the diaphragm via a trigger (threshold value switch). In contrast thereto, in cameras with an automatic diaphragm, it has been proposed to store a voltage analogous to the diaphragm in the storage means and to derive a rising voltage from the moving diaphragm and to stop the shutter in its operation when these two voltages are identical. Besides, it has also been suggested to invert the diaphragm-analogous voltage prior to storage and to have the voltage yielded by the diaphragm reach only the complementary value.
The automatic timing with preselected diaphragm is preferred by many newly available instruments, because it appears to be the logical choice from the technical viewpoint, especially with respect to the electronic system. No additional mechanical parts are required for the chronological change of the delay time of an electronically controlled shutter, while an automatic disphragm setting demands in some way or another the adjustment of a mechanical entity. Additionally, the diaphragm setting range comprises only about half as many light values as the time range of an electronic shutter. On the other hand, however, the automatic diaphragm is preferred by a majority of photographers. Therefore, there is a need for a camera wherein the user can switch over between automatic timing and automatic diaphragm. However, such a change-over possibility requires a considerable technical expenditure which cannot be tolerated in view of the small size of a photographic camera, especially a miniature camera.